PSI - Issue 30

N.A. Makhutov et al. / Procedia Structural Integrity 30 (2020) 87–92 N.A. Makhutov et al. / Structural Integrity Procedia 00 (2020) 000–000

90 4

Casting defect in the form of internal shrinkage with the area of 35 mm 2

2011

The most sensitive to the influence of these factors are stress concentration areas (interfaces of parts, casting defects, etc.). At ambient temperatures below -30 °C, the cold- and crack resistance, impact strength of the cast steel of which a side frame is made (Fig. 2, 3) are noticeably reduced, and at the same time, the running gear vertical and horizontal dynamics increases because of an increase of track rigidity. The analysis of operational data relating to the failure of rails showed that contact-fatigue defects steadily occupy an important place (Fig. 4). Contact-fatigue stresses in the rail increase with a gradual accumulation of defects in its head surface layer that deteriorates during operation. At the same time, the rail fatigue strength is significantly reduced, the metal percentage elongation is reduced by several times due to the depletion of plastic properties as a result of a repeated cold-work hardening. This leads to the formation of metal shelling up to 4 mm deep and longitudinal cracks up to 8 mm deep, followed by the development of transverse fatigue cracks. The direct dependence of their growth on the passed tonnage was also established. During static tests of specimens with cracks at decreasing the temperature, there is an increase in σ 0.2 and a decrease in σ C , K 1 C , ψ K and e i max (Fig. 3).

Fig. 2. The dependence of the impact strength of material St3ps on the temperature and probability of material failure.

Fig. 3. Temperature dependences of crack resistance and other mechanical properties of a low-alloy steel.